1. Field of the Invention
The present invention relates to a tire grip sensor, and more particularly to a highly reliable control system suitable for detecting a tire grip.
2. Description of the Related Art
In addition to known passive safety techniques, active safety techniques have been developed for the purpose of reducing traffic accidents. The active safety techniques include an ABS (Antilock Braking System), a technique for detecting a collision and alleviating injury, a technique for stabilizing a vehicle, and control for braking, driving and steering with an X-by-Wire system.
To realize those active safety techniques, it is essential to detect a tire grip (frictional) force. As one of known methods for detecting tire grip conditions while a vehicle is running, Patent Reference 1; JP-A-2001-4650, for example, discloses a method of determining an estimated value based on a steering angle, a yaw rate sensor, etc. Another method of directly determining a gradient of frictional forces from a change in resonance gain of a tire-body system is proposed in Non-Patent Reference 1; Katsuhiro Asano, et al., “Wheel Vibration Phenomenon and Maximization Control of Braking Force”, Toyota Central R&D Labs., Inc., R&D Review Vol. 34, No. 2, 1999.6, (http://www.tytlabs.co.jp/japanese/review/rev342pdf/342—027a sano.pdf), Patent Reference 2; JP-A-10-2813, and Patent Reference 3; JP-A-8-132831.